1. Field of the Invention
The present invention relates to non-contacting conveyance equipment used in rotation etc.
2. Description of the Related Art
In recent years, as the use of integrated circuit cards, smart cards, etc., has increased, and the uses and types of such products have become more diverse, wafers have become thin, and the diameter of wafers has increased. Wafers 0.5 mm thick and 10 inches in diameter have been developed. Such thin and large wafers curve or crack easily.
Thus it is difficult to avoid cracking a wafer when conveying it to be processed or moving it within a processing stage for manufacturing integrated circuits. That is, the mechanical integrity of a wafer decreases as the diameter of the wafer increases, or as the thickness of the wafer decreases. For this reason, non-contacting conveyance equipment is proposed. Non-contacting conveyance equipment holds and conveys a wafer by non-contacting means using air, nitrogen gas, and the like, and such means are already in practical use.
For example, in JP 11-254369, air is introduced through an air inlet into a chamber. Within the chamber, the air flows about a rotational flow generating plate and is then deployed to the inside of a bell mouth. The air enters the bell mouth while turning, and is directed out of the bell mouth over a flat surface at the parameter of the bell mouth. An object to be carried rests within the bell mouth.
One problem associated with the device disclosed in JP11-254369 is that, because air is introduced from an inlet above the bell mouth, a large amount of air is necessary. In addition to consuming excess energy, increased air flow can be detrimental in a semiconductor clean room. That is, currents of air within the clean room can stir up dust and other debris. Dust and debris can cause defects in the circuits printed on the semiconductor wafers.
Moreover, with the non-contacting conveyance equipment proposed in JP11-254369, the power of attracting and holding a conveyed object by causing a fluid to swirl can be improved because the feeding mouth, revolution room, and bell mouth of air allow free passage for the conveyed object, are complicated in structure and the equipment is costly to manufacture.
Moreover, since the equipment of JP11-254369 is structurally complicated, miniaturization is difficult, the action range of the equipment is limited, and the equipment is problematically inflexible.
Furthermore, owing to the complicated structure of a method using air, passage resistance becomes great. Therefore, in order to maintain sufficient attraction power, a lot of air needs to be deployed, thereby decreasing energy efficiency. Moreover, when a lot of air is circulated in a clean room, displaced dust becomes a problem.